Sleep Makes Memories More Accessible, Vivid

You may have heard that sleeping protects memories from being forgotten. According to new research, however, sleep can also make those memories easier to access. The results of a new study from the University of Exeter and the Basque Centre for Cognition, Brain and Language suggest that after sleep we are more likely to recall facts we could not remember before.

The beneficial impact of sleep on memory is well established, and the act of sleeping is known to help us remember the things that we did, or heard, the previous day. The idea that memories could also be sharpened and made more vivid and accessible overnight, however, is relatively new.

Nicolas Dumay of the University of Exeter explains: “Sleep almost doubles our chances of remembering previously unrecalled material. The post-sleep boost in memory accessibility may indicate that some memories are sharpened overnight. This supports the notion that, while asleep, we actively rehearse information flagged as important.”

Dumay believes that this memory boost comes from the hippocampus, an inner structure of the temporal lobe, unzipping recently encoded episodes and replaying them to regions of the brain originally involved in their capture – this would lead a person to effectively re-experience the major events of the day.

Participants in the study were taught a series of made-up words, asked to recall them after a 12-hour day, then asked to recall them again after a night’s sleep. Overwhelmingly, when the study participants forgot information over the course of 12 hours of wakefulness, a night’s sleep was shown to promote access to memory traces that had initially been too weak to be retrieved. The researcher team found that, compared to daytime wakefulness, sleep helped rescue unrecalled memories even more than it prevented memory loss.

The key distinction was between those word memories which participants could remember at both the immediate test and the 12-hour retest, and those not remembered at first test, but eventually remembered at retest.

Nicolas Dumay is an experimental psychologist at the University of Exeter and an honorary Staff Scientist at the Basque Centre for Cognition, Brain and Language (BCBL), in Spain.

The study, entitled ‘Sleep not just protects memories against forgetting, it also makes them more accessible,’ is published in the journal Cortex.

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